Mu Ko Ang Thong National Marine Park was gazetted in 1980 to protect 102 square kilometres of limestone archipelago geology in the Gulf of Thailand. The park's 42 islands form a tight cluster 31 kilometres northwest of Koh Phangan, their sheer karst cliffs rising directly from shallow coral platforms and sheltered lagoons. Most islands remain uninhabited — no permanent settlements exist within park boundaries — and dense monsoon forest covers the steep interior slopes where macaques, monitor lizards, and dusky langurs move through the canopy. The park's most photographed feature is Talay Nai, an enclosed saltwater lagoon on Ko Mae Ko accessible only by a 250-metre vertical climb through exposed rock face and fixed rope sections. The lagoon sits 50 metres above sea level, separated from the open ocean by a thin limestone ridge, and its emerald water shifts colour hourly as sun angle and cloud cover change. Park regulations limit lagoon visits to 200 persons daily and require certified guides for the ascent. Ko Wua Talap, the park headquarters island, offers a second viewpoint trail — 430 metres of switchback stairs to a 240-metre summit — that reveals the full archipelago spread across the northern gulf horizon. Speedboat and yacht operators departing Thong Sala pier on Koh Phangan run daily services during the November-to-April dry season, when northeast monsoon winds drop below 15 knots and visibility exceeds 10 metres. Most itineraries include snorkelling stops at shallow coral gardens off Ko Tai Phlao and Ko Hin Dap, kayaking through mangrove channels on Ko Sam Sao, and a beach landing at Ko Wua Talap for the viewpoint hike. The 300-baht conservation fee per foreign adult funds trail maintenance, mooring buoy installation, and ranger patrols that enforce the park's no-fishing and no-anchoring zones. Semi-private yacht charters reduce group size to 12 passengers and add sunset departure slots that return to Koh Phangan after 18:00, though park land areas close at dusk regardless of vessel access.